The present invention relates to safety devices in a system for controlling the energization of a direct current motor for driving an electric vehicle, and more particularly relates to a brake switch for interrupting the system whenever the vehicle is unattended and to interlocking means which functions whenever a direction controlling switch has previously been left in a forward or reverse position by preventing energization of the motor until the direction controlling switch is first returned to a neutral position and then set for the desired direction of vehicle movement.
Electrically powered vehicles, such as battery operated trucks used in manufacturing facilities and warehouses, are frequently provided with a solid state control system. A typical system is disclosed in U.S. Pat. No. 3,562,617, issued on Feb. 9, 1971 in the names of Roger D. Meier and Philip H. Rusch. In control systems of the type herein contemplated, a main energization controlling silicon controlled rectifier is switched to a conductive state at regulated spaced time intervals by an adjustable periodic switching means, and is switched to a nonconductive state a predetermined time interval after it is switched to a conductive state. The switching of the main rectifier to a nonconductive state is accomplished by a commutating silicon controlled rectifier which is controlled by periodic switching means to deliver a charge on a capacitor through the main rectifier in a reverse direction to thereby commutate the main rectifier to its nonconductive state. While the circuit disclosed in the Meier et al patent application has been successfully used to control electric vehicles and to detect circuit malfunctions therein, further safety features are desirable such as an interrupting means to detect the absence of the operator of the vehicle to interrupt the system and interlocking means to prevent energization of the motor if a direction controlling switch has previously been left in a forward or reverse position until the switch is first returned to a neutral position and then set for the desired direction of vehicle movement.
The brake switch or so called dead man's control functions to render the control system inoperative thereby deenergizing the driving motor when the operator leaves the vehicle unattended. The interlocking means prevents the vehicle from starting in an undesired direction or at an excessive rate of acceleration which could endanger the operator or other people or objects.
It is therefore an object of the present invention to provide a brake switch or dead man's control in a system for controlling an electric vehicle to interrupt a motor energization controlling means whenever the vehicle is unattended.
Another object is to provide an interlocking means to prevent energization of the motor if a direction controlling switch has previously been left in a forward or reverse position until the switch is first returned to a neutral position and then set to the desired direction of vehicle movement.
Further objects and features of the invention will be readily apparent to those skilled in the art from the specification and appended drawing illustrating a preferred embodiment, in which a schematic wiring diagram of a direct current motor control system incorporating the features of the present invention is shown.